A known type of vehicular power seat slide device is disclosed in Japanese Patent Laid-Open Publication No. Hei. 9(1997)-142181 published on Mar. 3, 1998 without examination. This known vehicular power seat slide device includes a lower rail fixed to the vehicle body floor, an upper rail supporting a seat device and slidably mounted on the lower rail, a nut member fixed to the lower rail, a screw shaft rotatably supported on the upper rail and threadably engaged with the nut member, and a gear box provided on the upper rail and associated with the screw shaft and an electric driving source.
When the electric driving source is turned on, the resulting rotation of the output shaft is transmitted to the screw shaft by way of the gear box. The screw shaft is thus rotated relative to the nut member, thereby moving the upper rail relative to the lower rail. As a result, the position of the seat device in the vehicle lengthwise direction is adjusted relative to the vehicle body floor.
In addition, the gear box is pivoted by a pin to a bracket which is provided at a front end portion of the upper rail, and a damper is disposed between the gear box and a flange formed at the front end portion of the upper rail. When a load in the direction of the vehicle lengthwise direction is applied to the upper rail, the load is transmitted from the screw shaft to the gear box due to the fact that the upper rail is restricted to the lower rail by the thread engagement between the nut member and the screw shaft. The resultant load is received at the flange after being absorbed partially in the damper. Thus, the rigidity of the vehicle power seat slide device is maintained.
However, the vehicular power seat slide device is susceptible of certain improvements. The gear box is held by the upper rail in a rotatable manner and this causes a rotation of the gear box relative to the upper rail when a load is applied to the gear box in the vehicle lengthwise direction. Thus, upon collision of the vehicle, if the load applied to the upper rail is extremely large, the screw shaft may be deformed. In the worst case, the gear box may be broken.
In light of the foregoing, a need exists for a vehicular power seat slide device that is not as susceptible to the same drawbacks mentioned above.